Synchronized array power oscillator with leg inductors

ABSTRACT

An electronic high frequency induction heater driver, for a variable spray fuel injection system, uses a scalable array of zero-voltage switching oscillators that utilize full and half-bridge topology with inductors between semiconductor switches wherein the semiconductor switches are synchronous within each bridge for function, and each bridge is synchronized for function along the entire array. The induction heater driver, upon receipt of a turn-on signal, multiplies a supply voltage through a self-oscillating series resonance, wherein one component of each tank resonator circuit comprises an induction heater coil magnetically coupled to an appropriate loss component so that fuel inside a fuel component is heated to a desired temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional of, and claims priority to theApr. 22, 2011, filing date of, U.S. provisional patent application Ser.No. 61/478,383, entitled Synchronized Array Power Oscillator with LegInductors, the entire content of which is incorporated herein byreference.

And this application is related to the following U.S. non-provisionalpatent applications filed on the same day as this application:

Synchronous Full-Bridge Power Oscillator with Leg Inductors, invented byPerry Czimmek, and identified by Attorney Docket Number 2011P00689US01;

Synchronous Full-Bridge Power Oscillator, invented by Perry Czimmek, andidentified by Attorney Docket Number 2011P00690US01;

Synchronized Array Bridge Power Oscillator, invented by Perry Czimmekand Mike Hornby, and identified by Attorney Docket Number2011P00691US01;

Variable Spray Injector with Nucleate Boiling Heat Exchanger, inventedby Perry Czimmek and Hamid Sayar, and identified by Attorney DocketNumber 2011P00693US01; and

Adaptive Current Limit Oscillator Starter, invented by Perry Czimmek,and identified by Attorney Docket Number 2011P00694US01.

BACKGROUND

Embodiments of the invention relate generally to heated tip fuelinjectors, and more particularly, to controlling and driving aninduction-heated fuel injector.

There is a continued need for improving the emissions quality ofinternal combustion engines. At the same time, there is pressure tominimize engine crank times and time from key-on to drive-away, whilemaintaining maximum fuel economy. Those pressures apply to enginesfueled with alternative fuels such as ethanol as well as to those fueledwith gasoline.

During cold temperature engine start, the conventional spark ignitioninternal combustion engine is characterized by high hydrocarbonemissions and poor fuel ignition and combustibility. Unless the engineis already at a high temperature after stop and hot-soak, the crank timemay be excessive, or the engine may not start at all. At higher speedsand loads, the operating temperature increases and fuel atomization andmixing improve.

During an actual engine cold start, the enrichment necessary toaccomplish the start leaves an off-stoichiometric fueling thatmaterializes as high tail-pipe hydrocarbon emissions. The worstemissions are during the first few minutes of engine operation, afterwhich the catalyst and engine approach operating temperature. Regardingethanol fueled vehicles, as the ethanol percentage fraction of the fuelincreases to 100%, the ability to cold start becomes increasinglydiminished, leading some manufacturers to include a dual fuel system inwhich engine start is fueled with conventional gasoline and enginerunning is fueled with the ethanol grade. Such systems are expensive andredundant.

Another solution to cold start emissions and starting difficulty at lowtemperature is to pre-heat the fuel to a temperature where the fuelvaporizes quickly, or vaporizes immediately (“flash boils”), whenreleased to manifold or atmospheric pressure. Pre-heating the fuelreplicates a hot engine as far as fuel state is considered.

A number of pre-heating methods have been proposed, most of whichinvolve preheating in a fuel injector. Fuel injectors are widely usedfor metering fuel into the intake manifold or cylinders of automotiveengines. Fuel injectors typically comprise a housing containing a volumeof pressurized fuel, a fuel inlet portion, a nozzle portion containing aneedle valve, and an electromechanical actuator such as anelectromagnetic solenoid, a piezoelectric actuator or another mechanismfor actuating the needle valve. When the needle valve is actuated, thepressurized fuel sprays out through an orifice in the valve seat andinto the engine.

One technique that has been used in preheating fuel is to inductivelyheat metallic elements comprising the fuel injector with a time-varyingmagnetic field. Exemplary fuel injectors having induction heating aredisclosed in U.S. Pat. No. 7,677,468, U.S. Patent Application No's:20070235569, 20070235086, 20070221874, 20070221761 and 20070221747, thecontents of which are hereby incorporated by reference herein in theirentirety. The energy is converted to heat inside a component suitable ingeometry and material to be heated by the hysteretic and eddy-currentlosses that are induced by the time-varying magnetic field.

The inductive fuel heater is useful not only in solving theabove-described problems associated with gasoline systems, but is alsouseful in pre-heating ethanol grade fuels to accomplish successfulstarting without a redundant gasoline fuel system.

Because the induction heating technique uses a time-varying magneticfield, the system includes electronics for providing an appropriate highfrequency alternating current to an induction coil in the fuel injector.

Conventional induction heating is accomplished with hard-switching ofpower, or switching when both voltage and current are non-zero in theswitching device. Typically, switching is done at a frequency near thenatural resonant frequency of a resonator, or tank circuit. Theresonator includes an inductor and capacitor that are selected andoptimized to resonate at a frequency suitable to maximize energycoupling into the heated component.

The natural resonant frequency of a tank circuit is fr=1/(2π√{squareroot over (LC)}), where L is the circuit inductance and Cis the circuitcapacitance. The peak voltage at resonance is limited by the energylosses of the inductor and capacitor, or decreased quality factor, Q, ofthe circuit. Hard-switching can be accomplished with what are calledhalf-bridge or full-bridge circuits, comprising a pair or two pairs ofsemiconductor switches, respectively. Hard-switching of power results inthe negative consequences of switching noise, and high amplitude currentpulses at resonant frequency from the voltage supply, or harmonicsthereof. Also, hard switching dissipates power during the linear turn-onand turn-off period when the switching device is neither fullyconducting nor fully insulating. The higher the frequency of ahard-switched circuit, the greater the switching losses.

The preferred heater circuit therefore provides a method of driving aheated fuel injector wherein switching is done at the lowest possibleinterrupted power. This heater circuit was disclosed in U.S. Pat. No.7,628,340, Title: Constant Current Zero-Voltage Switching InductionHeater Driver for Variable Spray Injection. Ideally, energy should bereplenished to the tank circuit when either the voltage or the currentin the switching device is zero. It is known that the electromagneticnoise is lower during zero-voltage or zero-current switching, and islowest during zero-voltage switching, this is the method of U.S. Pat.No. 7,628,340. It is also known that the switching device dissipates theleast power under zero switching. That ideal switching point occurstwice per cycle when the sine wave crosses zero and reverses polarity;i.e., when the sine wave crosses zero in a first direction from positiveto negative, and when the sine wave crosses zero in a second directionfrom negative to positive.

It is preferable to reduce the size of inductive components and in somecases, eliminate the impedance-matching transformer, while maintainingthe minimum necessary connections to the inductive heater coil on theinjector. It is further preferable to reduce the overall quantity ofcomponents in repetitive function circuits by combining compatiblefunctions of adjacent circuits. The Embodiments of the inventioncontinue to provide for the elimination of the hard-switching and itsnegative consequences, replace it with zero-voltage switching, andfurther apply this method in a full-bridge topology while advantageouslyeliminating the impedance matching transformer and overcoming thedifficulties of alternative solutions.

The elimination of the impedance matching transformer and elimination ofthe center-tap of the induction heating coil such that only twoconductors are used for transmission of power has been disclosedseparately. Additionally, forced current sharing through the inductionheating coil while allowing for flexibility and suitable inductance andampere-turns of the induction heater coil has been disclosed separately.

BRIEF SUMMARY

Embodiments of the invention reduce the number of full-bridgesemiconductor switches by replacing additional full-bridges withsynchronized half-bridges and a corresponding reduced number ofsemiconductor switches. An embodiment of the invention uses two pairs ofcomplimentary pairs of power switching transistors in a full-bridge, orH-bridge, configuration, subsequent complimentary pairs formhalf-bridges sharing the adjacent half-bridge to create a sequence ofvirtual full bridges synchronized with the original full-bridge poweroscillator.

The deviation from a full-bridge driver is that the bridgeadvantageously further prevents shoot-through current by distributinginductance in the form of leg inductors within the bridge to form aplurality of constant-current inductors, and the load section of theconventional full bridge is replaced with the resonant tank circuit. Theoscillator-synchronous inherent zero-switching topology that drives thegates of the complimentary pairs of transistors in alternating sequenceof diagonal pairs also deviates from a conventional full-bridge driver.

Additionally, the tank-replenishment current passes through theinduction heater coil and at least one leg inductor within each bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified electrical schematic diagram showing asynchronized array comprised of a full H-bridge at the top and thencascading half-bridges with leg inductors disposed within each bridgeand without a transformer and without a center-tap inductive heater coilin accordance with embodiments of the invention.

FIG. 2 is a simplified electrical schematic diagram showing asynchronous bridge oscillator with leg inductors adjacent to high-sideswitches and without a transformer and without a center-tap inaccordance with embodiments of the invention.

FIG. 3 a shows current shoot-through without high-side switches and FIG.3 b shows a full H-bridge with inductors in bridge legs that preventsshoot-through current in accordance with embodiments of the invention.

DETAILED DESCRIPTION

Ideally, energy should be replenished to the tank circuit when eitherthe voltage or the current in the switching device is zero. Theelectromagnetic noise is lower during zero-voltage or zero-currentswitching, and is lowest during zero-voltage switching. The switchingdevice dissipates the least power under zero switching. That idealswitching point occurs twice per cycle when the sine wave crosses zeroand reverses polarity; i.e., when the sine wave crosses zero in a firstdirection from positive to negative, and when the sine wave crosses zeroin a second direction from negative to positive.

Embodiments of the invention eliminate hard-switching and its negativeconsequences, and replace it with zero-voltage switching in afull-bridge configuration. The integrated functions of the synchronousfull-bridge power oscillator heater driver of the invention will beexplained with reference to FIG. 2, which is a simplified representationof a circuit in accordance with embodiments of the invention with manyof the basic components not shown for clarity. Specific or generalvalues, ratings, additions, inclusion or exclusion of components are notintended to affect the scope of the invention.

L1 may be located inside a fuel injector. L1 is an induction heater coilthat provides ampere-turns for induction heating a suitablefuel-injector component.

A synchronous full-bridge power oscillator in accordance withembodiments of the invention may include R1, R2, D1, D2, Q1, Q2, Q3, Q4,L2, L3, C1 and L1. Q1 and Q2 are enhancement-type N-MOSFET (N-channelMetal-Oxide-Semiconductor Field-Effect Transistor) switches thatalternatively connect tank resonator, C1 and L1, circuit to ground and,when each is turned on in the respective state, enables current to flowthrough induction heater coil and ground. Q3 and Q4 are enhancement-typeP-MOSFET (P-channel Metal-Oxide-Semiconductor Field-Effect Transistor)switches that alternatively connect tank resonator, C1 and L1, circuitto the voltage supply. Replenishment current for the tank passes througheither L2 or through L3, and with Q1 and Q2 in the appropriate state,enable current to flow through induction heater coil.

C1 and L1 are the tank resonator capacitor and tank resonator inductor,respectively, of a resonant tank circuit. The resonant frequency of thetank circuit is fr=1/(2π√{square root over (LC)}), where L is the heatercoil inductance L1, and Cis the capacitance of tank capacitor C1. Thepeak voltage in the tank circuit is set by V_(out)=π*V_(in) where V_(in)is the supply voltage. The current level in the tank circuit isdetermined from the energy balance of

${\frac{1}{2}{LI}^{2}} = {\frac{1}{2}{{CV}^{2}.}}$

The zero-switching power oscillator circuit is self-starting inoscillation, but may be forced into oscillation by selectivelysequencing the switching of Q1-Q4 in a full-reversing H-bridge strategy.The complimentary pairs, or here, the pairs of transistors that areflowing current between the MOSFET ‘drain’ and ‘source’ at the same timeare Q3 and Q2 or Q4 and Q1. It is not desirable to have Q1 flowingcurrent when Q3 flows current, and likewise, it is not desirable to haveQ2 flowing current when Q4 flows current. L2 and L3 provide thistransient separation during state change of the H-bridge transistors. L2and L3 additionally isolate the resonant tank from the voltage source.When Q3 is flowing current, current passes through the induction heatercoil and then through Q2 to ground. When Q4 is flowing current, currentpasses through the induction heater coil in the reverse direction aswhen Q3 was flowing current, and then through Q1 to ground, this is‘full-reversal’ of current.

A MOSFET is a device that has a threshold for an amount of Coulombcharge into the gate, which is drain-source current-dependent.Satisfying the charge threshold enhances the device into an ‘on’ state.First and second gate resistors R1, R2 supply the gate charging currentto first and second legs of the H-bridge. R1 supplies current to gatesof Q1 and Q3, R2 supplies current to the gates of Q2 and Q4,respectively, and R1, R2 limit the current flowing into first and secondgate diodes D1, D2, respectively. Q3 and Q4, P-MOSFET conduct betweendrain and source when source is more positive than gate. Q1 and Q2,N-MOSFET conduct between drain and source when source is more negativethan gate.

The loading caused by the resistive and hysteretic loss of the heatedcomponent reflects back as a loss in the resonant tank circuit. Thatloss is replenished by current flowing from a current source inductoreither L2 or L3, from the voltage supply applied by the respective topbridge transistors, Q3 and Q4. Depending on the state of reversal of theH-bridge in which the current flows, the current will flow eitherthrough Q3 or Q4 and then through induction heater coil L1. L2 or L3will supply current to the tank circuit from the energy stored in theirrespective magnetic fields. That energy is replenished from the supplyvoltage as a current that constantly flows into L2 or L3 from thevoltage source through Q3 or Q4, respectively, during operation of thesynchronous full-bridge power oscillator.

If current is flowing through Q3, as determined by the polarity of thesine wave half-cycle at that time, then the conduction to ground from Q2drain-to-source is pulling charge out of the gate of Q3 and Q1 throughforward biased D1. Q1 is also now not conducting and does not pull thegate charge out of Q4 and Q2 to ground through D2. Meanwhile, R1 drawscurrent from the supply voltage. But the IR drop across R1 cannot chargethe gate of Q3 and Q1 with the gate shunted to ground by conductionthrough Q2.

When the sine wave crosses zero, then Q3 becomes reverse biased andconducts through the internal intrinsic diode to reverse-bias D1. D1stops conducting current away from the Q3 and Q1 gate, and R1 can chargethe gate of Q3 and Q1, which stops conduction in Q3 and startsconduction in Q1 to begin conducting current for the continuing sinehalf-cycle. Q1 also pulls the gate charge out of Q2 and Q4 to groundthrough D2 and holds Q2 in a non-conducting state which continues toallow R1 to enhance Q1. And Q4 conducts.

That process repeats as the sine wave alternates polarity, crossing zeroin a first direction from negative to positive, and then in a seconddirection from positive to negative. This generates full-reversal ofcurrent in L1, the induction heater coil. Current continues to bereplenished in the tank circuit from L2 or L3. An IGBT (Insulated GateBipolar Transistor) device can replace the N-MOSFET in this embodimentif the intrinsic diode of the N-MOSFET is represented by the addition ofan external diode across the drain and source of the IGBT.

FIG. 1 shows an expanded circuit of cascaded half-bridges that operatesin accordance with the principles of operation of the full-bridge asdescribed above and in reference to FIG. 2. Relative to FIG. 2, FIG. 1shows two additional induction heater coils and two correspondingadditional half bridges. In the embodiment shown in FIG. 2, theinduction heater coils and the half bridges are arranged such that eachinduction heater coil, IHC1-IHC3, is driven by a corresponding pair ofhalf bridges, HB1 and HB2 drive IHC1; HB2 and HB3 drive IHC2; and HB3and HB4 drive IHC3.

FIG. 3 a shows current shoot-through without high-side switches and FIG.3 b shows a full H-bridge, with inductors in bridge legs, that preventsshoot-through current in accordance with embodiments of the invention byforcing current to pass through an induction heater coil of a fuelinjector, for example.

The foregoing detailed description is to be understood as being in everyrespect illustrative and exemplary, but not restrictive, and the scopeof the invention disclosed herein is not to be determined from thedescription of the invention, but rather from the claims as interpretedaccording to the full breadth permitted by the patent laws. For example,while the synchronized array power oscillator of the invention isdescribed herein driving an induction heater coil for the heater in aninternal combustion engine fuel injector, the driver may be used todrive other induction heaters in other applications. It is to beunderstood that the embodiments shown and described herein are onlyillustrative of the principles of the present invention and that variousmodifications may be implemented by those skilled in the art withoutdeparting from the scope and spirit of the invention.

1. A synchronized array power oscillator for an electronic inductionheater driver, the synchronized array power oscillator comprising: anexpandable array of bridge circuit topology comprising high-side andlow-side semiconductor switches; a resonant tank circuit electricallyconnected between legs of the bridge in the topological location of aconventional H-bridge load, wherein the resonant tank circuit includesat least one induction heater coil; at least two leg inductors, eachelectrically in series with an adjacent high-side switch and low-sideswitch within the bridges; wherein bridge switch timing is determined bya synchronized frequency of resonant tank circuits.
 2. The synchronizedarray power oscillator of claim 1, wherein the leg inductors are betweenthe resonant tank circuit and the high-side switches to source currentto the resonant tank circuit from a voltage source.
 3. The synchronizedarray power oscillator of claim 1, wherein the leg inductors are betweenthe resonant tank circuit and the low-side switches to sink current fromthe resonant tank circuit to an absolute voltage sink having a voltagethat is less than the voltage source.
 4. The synchronized array poweroscillator of claim 1, wherein bridge synchronization is accomplishedthrough rectifier diodes sinking charge from one leg of a bridge to anopposite leg of the bridge.
 5. The synchronized array power oscillatorof claim 1, wherein bridge synchronization is accomplished throughresistors sourcing charge from the voltage supply.
 6. The synchronizedarray power oscillator of claim 1, wherein an inductance of each of theat least two leg inductors is greater than an inductance of theinduction heater coil.
 7. The synchronized array power oscillator ofclaim 1, wherein an inductance of each of the at least two leg inductorsis more than twice an inductance of the induction heater coil.